Although the administration of drugs by hygroscopic aerosol inhalation is a widely used procedure, with even greater unused potential, this form of therapy at the present time is much more of an art than a science. It is difficult to control the drug dosage adminstered. One also does not know what drug concentrations in the aerosolized solutions are optimal, what temperature or humidity is best in the aerosol generator, or what breathing modes should be used to selectively dose upper, middle or lower airways. The research proposed here seeks to answer these questions by using a combination of theory and experiments with a physical bronchial model and a selected number of human lungs obtained at autopsy. Hygroscopic aerosol deposition and transport studies on a physical model have never been done before. Use of the physical model requires a knowledge of dimensional analysis and dynamic scaling to select those parameters which are most important in controlling particle deposition in the various lung regions. By matching these parameters as closely as possible in the model and the real lung, a large amount of local detailed particle transport and deposition data can be obtained for various regions of the bronchial tree. These data, together with those obtained from theoretical calculations of aerosol particle growth and evaporation, can be used to develop optimal modes of therapy which can be further evaluated by controlled clinical trials.